Conventional piston dampers include MR dampers having a tube containing an MR fluid and having an MR piston assembly including a piston which slideably engages the tube and including a rod which has a first end attached to the piston and a second end extending outside the tube. The MR fluid passes through an MR passageway (i.e., a magnetically energizable passageway) of the MR piston. Exposing the MR fluid in the orifice to a varying magnetic field, generated by providing a varying electric current to an electric coil of the MR piston, varies the damping effect of the MR fluid in the MR passageway providing variably-controlled damping of relative motion between the MR piston and the tube. The electric current is varied (including turning off the electric current) to accommodate varying operating conditions, as is known to those skilled in the art. The tube and the rod are attached to separate structures to dampen relative motion of the two structures along the direction of piston travel. The damping from the MR passageway is the same for jounce (compression of the damper) and rebound (extension of the damper) for the same value of electric current applied to the electric coil of the MR piston.
A known design includes an MR piston having an MR passageway and a bypass passageway (i.e., a magnetically non-energizable passageway). In one known application, the MR damper is employed as a vehicle suspension damper to control vehicle ride and handling including damping during jounce and rebound. An orifice disc having a single orifice is positioned between the bypass passageway and a through passageway in the distal MR piston end plate of the MR piston. The damping from the bypass passageway is the same for jounce and rebound. A tapered MR passageway design is known which provides different damping for jounce and rebound for higher piston velocities. Externally-mounted apparatus having a bypass passageway with a spring-biased blow-off disc is known, wherein the apparatus is radially-outwardly mounted to the MR piston to provide different damping for jounce and rebound for higher piston velocities.
What is needed is an improved magnetorheological piston having a bypass passageway.